The goal of this patch was to refactor NumberFormat parameter handling
to be usable by a PluralRules implementation. Along the way, I found
and fixed a couple minor issues where options handling differed from
the specification, and removed some dead code. Regression tests are
added as test262 tests. With this change, the overall flow more closely
resembles the specification plus this editorial change which is out
for review: https://github.com/tc39/ecma402/pull/130/files

BUG=v8:6015,v8:6016
R=yangguo,jungshik

Review-Url: https://codereview.chromium.org/2717613005
Cr-Commit-Position: refs/heads/master@{#44571}